Polishing apparatus for notch portion of wafer

Abstract: Apparatus (1) for polishing a notch (32) on the periphery of a wafer (W) comprises: a table (2) for supporting the wafer; buff (7), adapted to polish the notch, which is rotatable about a first axis substantially parallel to the surface of the wafer; means (8) for rotating the buff; means (9) for supporting the buff; means (10) for adjusting the pressure applied by the buff to the notch; and means (4,4a,5,6) for rotating the table about a second axis which is substantially parallel to the first axis, so that the applied pressure acts on the bottom wall of the wafer, in the notch, in a direction substantially perpendicular to the surface of said bottom wall.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a polishing apparatus for a notch portion formed on the periphery of a wafer (hereinafter, which is simply called "a polishing apparatus") which is used for positioning adjustment or crystal orientation adjustment of the wafer. Description of Related Art Generally, a photolithographic technique is used for the purpose of forming a pattern for a semiconductor integrated circuit in a single crystal of Si, compound semiconductor or the like (hereinafter, which is simply called "a wafer"). Such an application of the photolithographic technique requires a precise positioning adjustment and a precise crystal orientation adjustment. For these requirement, a linear portion is generally made on one side of the periphery of the wafer in order to use the linear portion as a standard for the positioning adjustment and the crystal orientation adjustment. This linear portion of the wafer is called an orientation flat. When such an orientation flat is formed on the wafer, a portion of the periphery of the wafer is cut off linearly. Therefore, the area of the cut portion of the wafer is large, so the number of semiconductor chips which can be obtained from a wafer decrease. As a result, according to such a conventional method in which an orientation flat is formed on a wafer, it is impossible to effectively utilize an expensive wafer. The conventional method has another problem in that it is difficult to treat wafers when each of the wafers has a large diameter and an orientation flat, so the wafers are not properly in balance, for example, on a work using a spin dryer or the like in which the wafers are dried by a centrifugal force due to a high speed rotation. Recently, in order to solve the above problems, another method has been used in which a small notch having a circular arc shape or a shape of a character "V" in plan view is formed in a portion of the periphery of each wafer. In this method, positioning and crystal orientation adjustments of the wafer are carried out by using the notch. Such a notch is formed by using a grinding wheel 31 or the like, as shown in FIG. 3. That is, the notch portion 32 is formed by making the grinding wheel 31 press into a portion of the periphery of the wafer W and by grinding the portion, as shown in the plan view of FIG. 4. FIG. 5 is a vertically cross-sectional view showing the wafer W cut along the line 5-5 of FIG. 4. The wall of the wafer W in the notch portion 32 swells into a curve toward the outside in the middle of vertical direction, as shown in this Figure. A further apparatus for grinding a notch on the periphery of a wafer is known from US-A-5 185 965. It comprises a table for supporting the wafer, a grinding wheel, adapted to grind the notch, which is rotatable about an axis substantially parallel to the surface of the wafer, and means for rotating the grinding wheel. In a photolithographic process, particles may be a main impact to form fine patterning for semiconductor devices. Therefore, in order to minimize the amount of the particles, a clean room having a higher cleanliness is required. Furthermore, it is desired to suppress generation of particles from the wafer as less as possible. In order to solve the above problems, it is necessary to polish the wall of the wafer in the notch portion 32 and thereby to prevent generation of particles when the wall of the wafer in the notch portion 32 is in contact with a hard pin for crystal orientation adjustment of the wafer. However, the width of the notch portion 32 to be formed is smaller than that of the orientation flat. As mentioned above, the notch portion 32 has a circular arc shape or a shape of a character "V" in plan view and the wall of the wafer W in the notch portion 32 has a complicated shape. Therefore, it is difficult to polish this portion. SUMMARY OF THE INVENTION The present invention was developed in view of the above-described problems. An object of the present invention is to provide an apparatus which can effectively polish the wall of the wafer in the notch portion. The invention is defined in claim 1. It is to be noted here that the bottom wall of the wafer in the notch portion (which, hereinafter, is simply called "the bottom wall") designates the back wall of the wafer nearest to the center of the wafer W in the notch portion. In the polishing apparatus of the present invention, the rotary buff is pressed against the notch portion of the wafer supported on the table, by the adjusting member such as a cylinder device, and the rotary buff is rotated on the center axis thereof by the first rotating member such as an electric motor. Further, the table is turned around a predetermined axis which is approximately parallel with the rotary axis of the rotary buff by the second rotating member such as a pulse motor so that the applied pressure from the rotary buff acts on the bottom wall in a direction approximately perpendicular to the surface of the bottom wall. Consequently, since the rotating buff presses the bottom wall, while following on the surface of the wall, the bottom wall can be polished. The pressure applied to the bottom wall can be always maintained constantly in spite of the attitude or angle of the wafer by the adjusting member. Accordingly, it is possible to obtain a bottom wall having an excellent polishing surface. Preferably, the table has a pulse motor which can reciprocally rotate the wafer supported on the table around the center thereof in clockwise and counterclockwise directions within a predetermined small angle. Accordingly, it is possible to make the wafer reciprocally rotate around the center thereof in clockwise and counterclockwise directions within a predetermined small angle. So the side walls of the wafer in the notch portion can be polished. As a result, the whole wall, i.e., not only the bottom wall but also the side walls, of the wafer in the notch portion can be excellently polished. Preferably, the table may be communicated with a vacuum absorption system, so that the wafer can be held on the table by vacuum absorption. The second electric motor may be a pulse motor. The table may be preferably supported on a crank having a pair of crankshafts. One of the crankshafts may be connected with the second electric motor so that the table can be turned around the crankshaft through the crank having the crankshaft, by means of the second motor. The other of the crankshafts may be supported by a bearing. The bearing and the second electric motor may be disposed so that the pair of crankshafts are on a straight line which is parallel with the plane of the surface of the wafer supported on the table. The wafer may be set on the table so that the straight line is substantially in contact with the notch portion of the wafer. Preferably, the polishing apparatus further comprises a linkage which has a first fixed link and a second link for supporting the rotary buff, and the second link may be provided so as to be movable like a seesaw on a shaft which is attached to an upper portion of a bracket erected on the first fixed link. The rotary buff and the first electric motor may be attached to one end of the second link, and the cylinder device may be disposed between an end of the first link opposite to the rotary buff and the other end of the second link. Preferably, the polishing apparatus further comprises a construction so that the table is relatively movable with respect to the crankshafts. An alkaline solution with dispersed colloidal silica may be supplied as a polishing agent into the notch portion of the wafer, during polishing. The cylinder device may be one selected from the group consisting of an air cylinder device, and a hydraulic cylinder device. The linkage holding the rotary buff may be preferably balanced with respect to a shaft which works as a fulcrum. The air-pressure in the cylinder device may be kept constant so that the pressure applied to the wall of the wafer in the notch portion is substantially maintained constantly in spite of the attitude or angle of the linkage. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: FIG. 1 is a perspective view showing an polishing apparatus for a notch portion of a wafer according to an embodiment of the present invention; FIG. 2 is a side view for explaining the polishing apparatus for the notch portion of the wafer as shown in FIG. 1; FIG. 3 is a perspective view showing a grinding wheel for grinding the notch portion of the wafer; FIG. 4 is a plan view showing a wafer having a notch portion; FIG. 5 is a vertically cross-sectional view taken along the line 5-5 in FIG. 4. PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the polishing apparatus according to the present invention will be explained with reference to the drawings. FIG. 1 shows an polishing apparatus according to an embodiment of the invention. In this Figure, numeral 1 denotes the polishing apparatus. The polishing apparatus 1 comprises a table 2 holding a wafer W thereon, and a pulse motor 3 which is attached to a crank 4 and can repeatedly make the table 2 reciprocally rotate in clockwise and counterclockwise directions within a predetermined small angle around the center thereof. A vacuum absorption system (not shown) is communicated with the table 2, so that the wafer W can be held on the table 2 by vacuum absorption. The table 2 is supported on a crank 4 with a pair of crankshafts 4a and 4a. One of the crankshafts 4a and 4a is supported by a bearing 5, and the other is connected with a pulse motor (a second motor) 6. The polishing apparatus 1 comprises a rotary buff 7 which is made of an elastic material, e.g., a synthetic resin such as foamed polyurethane or the like. The rotary buff 7 is connected with an electric motor (a first motor) 8 which makes the rotary buff 7 rotate, and is supported by a linkage 9. The rotary buff 7 can rotate around a shaft 7a which is parallel with the plane of the surface of the wafer W held on the table 2. The linkage 9 comprises a fixed first link 91 having a plate 91a and a pair of brackets 91b and 91b, and a second link 92. The pair of brackets 91b and 91b are erected at the middle on the plate 91a of the fixed first link 91. The second link 92 is provided so that the link 92 is movable like a seesaw on a shaft 92a which is provided to an upper portion of the brackets 91b and 91b. The rotary buff 7 and the electric motor 8 are provided on one end of the second link 92. An air cylinder device 10 is disposed between the other end of the second link 92 and a side of the fixed first link 91 opposite to the rotary buff 7. That is, the bottom of the air cylinder device 10 is mounted flexibly on the plate 91a, and the top end of a rod of the air cylinder device 10 is provided so as to form a turning pair with the second link 92. The air cylinder device 10 is communicated with an air supply and exhaust equipment and an air pressure control unit, which are not shown in the drawings. Next, procedure for polishing the notch portion 32 of the wafer W carried out by the polishing apparatus 1 of a notch portion will be explained. First, a wafer W is set on the table 2 by vacuum absorption or the like. When the wafer W is set on the table, the wafer W is set up so that the notch portion 32 of the wafer W is positioned on the straight line which connects the pair of crankshafts 4a and 4a. For properly setting up the wafer W, it is desired to previously and properly set up the relationship between the positions of the crankshafts 4a and 4a and the position of the table 2, or to provide a construction so that the table 2 can be relatively moved with respect to the crankshafts 4a and 4a. When the wafer W is set on the table 2, the rotary buff 7 is apart from the wafer W by using the air cylinder device 10. Next, the air cylinder device 10 is operated to press the rotary buff 7 against the wall of the wafer W in the notch portion 32. Then, the pressing portion of the peripheral surface of the rotary buff 7 is elastically deformed to a small extent, and thereby the rotary buff 7 comes in contact with the wafer W in a larger area of the notch portion 32. Thereafter, the table 2 is slowly turned around the crankshafts 4a by the pulse motor 6 so that the applied pressure from the rotary buff 7 acts on the swelling wall of the wafer W in the notch portion 32 in a direction perpendicular to the surface of the swelling wall, while the rotary buff 7 is rotated by the electric motor 8, as shown in FIG. 2. Consequently, the rotating buff 7 presses the wall of the wafer W in the notch portion 32, with following the surface of the wall, and thereby the wall can be polished. During this operation, a polishing agent, e.g., an alkaline solution with dispersed colloidal silica or the like, is supplied into the notch portion 32. The turning operation of the table 2 around the above mentioned pair of crankshafts 4a and 4a is carried out in a manner of reciprocating motion a predetermined number of times along the surface of the wafer W in the notch portion 32. The table 2 may be reciprocally rotated around the center thereof in clockwise and counterclockwise directions within a predetermined angle by the pulse motor 3, if necessary. Accordingly, the whole wall, i.e., not only the bottom wall but also the side walls, of the wafer W in the notch portion 32 can be polished. The above-described apparatus 1 for polishing a notch portion provides advantages as follows. According to the polishing apparatus of this embodiment, it is possible to effectively polish the wall of the wafer W in the notch portion, since the rotary buff 7 moves so as to follow the swelling curved surface of the wall in the notch portion 32. The table 2 is turned around the crankshafts 4a and 4a so that the applied pressure from the rotary buff 7 acts on the wall of the wafer W in the notch portion 32 in a direction perpendicular to the surface of the wall. The pressure can be constantly maintained by the second link 92 supporting the rotary buff 7 being in balance with respect to the shaft 92a and by keeping the air-pressure in the cylinder device 10 constant. Accordingly, it is possible to obtain an excellent polishing surface over the whole wall of the wafer in the notch portion. The table 2 can make the notch portion 32 of the wafer W reciprocally rotate in clockwise and counterclockwise directions within a predetermined angle by the pulse motor 3, on a plane perpendicular to the pressing direction of the rotary buff 7 around the center thereof. Accordingly, the whole wall of the wafer in the notch portion can be excellently polished. Although the present invention has been described in its preferred form with a certain degree of particularity, it should also be understood that the present invention is not limited to the preferred embodiment and that various changes and modifications may be made without departing from the scope of the appended claims. For example, the air cylinder device 10 is used in the above embodiment, however, a hydraulic cylinder device can be also used instead of the air cylinder device 10. As described above, since the rotary buff that is rotating moves simultaneously so as to follow the swelling curved surface of the wall of the wafer in the notch portion, it is possible to effectively polish the wall of the wafer in the notch portion. The pressure applied from the rotary buff to the wall of the wafer W in the notch portion can be constantly maintained by the link supporting the rotary buff being in balance with respect to the shaft and by keeping the air-pressure in the cylinder device constant. Accordingly, it is possible to obtain an excellent polishing surface. The table can make the notch portion of the wafer reciprocally rotate around the center thereof in a clockwise and a counterclockwise directions within a predetermined angle. Accordingly, the whole wall of the wafer in the notch portion can be excellently polished.

Claims: Apparatus (1) for polishing a notch (32) on the periphery of a wafer (W) comprising: a table (2) for supporting the wafer; a buff (7), adapted to polish the notch, which is rotatable about a first axis substantially parallel to the surface of the wafer; means (8) for rotating the buff; means (10) for adjusting the pressure applied by the buff to the notch; and means (4,4a,5,6) for rotating the table about a second axis which is substantially parallel to the first axis, so that the applied pressure acts on the bottom wall of the wafer, in the notch, in a direction substantially perpendicular to the surface of said bottom wall. Apparatus as claimed in claim 1, wherein the table can be reciprocally rotated around its centre, e.g. by a pulse motor (3), within a predetermined small angle, so that side-walls of the notch can be polished by the buff. Apparatus as claimed in claim 1 or claim 2, which additionally comprises a vacuum system adapted to hold the wafer on the table. Apparatus as claimed in any preceding claim, wherein the means for rotating the table about the second axis comprises a crank (4) having a pair of crankshafts (4a) of which one is preferably connected to a pulse motor (6) and the other is supported by a bearing (5). Apparatus as claimed in any preceding claim, wherein the second axis passes through the notch. Apparatus as claimed in any preceding claim, wherein the buff is supported by means (9) comprising an elongate member (92) hingedly mounted towards its centre on a fixed member (91). Apparatus as claimed in claim 6, wherein the buff and the pressure-adjusting means (10) are disposed at opposite ends of the elongate member. Apparatus as claimed in any preceding claim, wherein the pressure-adjusting means comprises a cylinder device (10), e.g. an air cylinder device or a hydraulic cylinder device. Apparatus as claimed in any preceding claim, wherein the periphery of the buff has a section that is almost the same shape as the shape of the notch in plan.

Inventors: HASEGAWA FUMIHIKO, ICHIKAWA KOICHIRO, NAKAMURA YOSHIO, OHTANI TATSUO, HASEGAWA, FUMIHIKO, ICHIKAWA, KOICHIRO, NAKAMURA, YOSHIO, OHTANI, TATSUO, HASEGAWA, FUMIHIKO, C/O SHIN ETSU HANDOTAI CO.,, ICHIKAWA, KOICHIRO, C/O FIJIKOSHI MACHINERY CORP., NAKAMURA, YOSHIO, C/O FIJIKOSHI MACHINERY CORP., OHTANI, TATSUO, C/O SHIN-ETSU HANDOTAI CO., LTD.
Applicants: FUJIKOSHI MACHINERY CORP, SHINETSU HANDOTAI KK, FUJIKOSHI MACHINERY CORPORATION, SHIN-ETSU HANDOTAI COMPANY LIMITED
Application year: 1994
Main classification: B24B9
IPC codes: H01L21, B24B9, B24B29